1. Field of the Invention
The present invention relates to a primary containment vessel of a boiling water type reactor, and, more particularly, to a primary containment vessel structured in such a manner that the performance of cooling the containment vessel can be improved at the time of a loss of coolant accident without a necessity of using a dynamic device such as a pump.
2. Description of the Prior Art
A primary containment vessel is arranged to hermetically surround a reactor pressure vessel which accommodates a core. An upper space surrounding the reactor pressure vessel in the primary containment vessel is called "a dry-well volume", while a space disposed in the lower portion of the primary containment vessel and filled with pool water is called "a suppression chamber". An outer pool filled with cooling water is formed around the suppression chamber of the primary containment vessel. The dry-well volume and the suppression chamber are connected to each other by a plurality of vent tubes, an end portion of the vent tube being opened in water enclosed in the suppression pool. A main steam line through which steam generated in the reactor pressure vessel passes and pipes into which coolant is introduced are disposed in the dry-well volume.
If the main steam line is burst in the primary containment vessel or the reactor pressure vessel is locally damaged, high temperature and high pressure cooling water becomes high temperature and high pressure steam and jets out in the dry-well volume. This is so-called a loss of coolant accident. The steam jetted out in the dry-well volume is introduced together with noncondensing gas (called hereinafter as gas) in the dry-well volume into water in the suppression pool via the vent tube, water being then cooled and condensed in the suppression pool, causing the pressure rise in the dry-well volume to be suppressed.
A primary containment vessel of the type described above has been disclosed in Japanese Patent Laid-Open No. 75594/1988. According to this disclosure, it is necessary for the convection of water in the pressure suppression pool to be induced and it is necessary for the outward heat transfer from the pressure suppression pool to be improved in order to have the primary containment vessel cooled effectively at the time of a loss of coolant accident. Therefore, the opening of the vent tube is disposed adjacently to the bottom of the suppression pool so as to cause water in the suppression pool to be convected by utilizing the buoyancy of heated water or gas in the suppression pool. However, a structure arranged such that the opening of the vent tube is, as described above, disposed deeply in the suppression pool encounters a problem in that a fear arises in that the water or gas in the suppression pool hits the ceiling of the suppression chamber since energy of the buoyancy of water or gas in the suppression pool becomes too large. Therefore, the suppression chamber must have a high ceiling, causing also the height of the primary containment vessel to be increased. As a result, the size of it inevitably become large.
If the vent tube outlet is disposed in the shallow water in the suppression pool, water close to the water surface convects since it is stirred. However, since deep water in the suppression pool is not stirred, it is difficult for the convection to occur. Therefore, water in the suppression pool below the bent tube outlet remains as it is with the initial temperature maintained, and a slight quantity water above the vent tube outlet becomes heated. Therefore, it is necessary for the diameter of the primary containment vessel to be enlarged in order to provide the heat transferring area necessary to remove the heating value at the time of the loss of coolant accident.
A suppression pool of a primary containment vessel disclosed in Japanese Patent Laid-Open No. 31837/1986 is arranged in such a manner that a distributing vane is locally provided for each of a plurality of the vent tube outlets in front thereof to disperse steam and gas jetted radially from the vent tube outlets in the circumferential direction so that the dynamic load to act on the primary containment vessel is reduced. However, this structure involves a problem in that it is difficult for water in the suppression pool to convect vertically.
A primary containment vessel has been disclosed in Japanese Patent Laid-Open No. 229390/1988 in which the core is immersed in water by utilizing the difference in the water heads from the water surface of water in the suppression pool to the core equalizing line at the time of a loss of coolant accident. According to this example, since water in the suppression pool cannot be easily convected and only upper hot water in the suppression pool is injected into the core, the cooling effect is unsatisfactory. Furthermore, since the high temperature water in the suppression pool cannot be easily transferred, the heat transference effect from the suppression chamber to the surrounding pool is insufficient.
A primary containment vessel has been disclosed in Japanese Patent Laid-Open No. 33697/1988 in which an annular suppression pool is disposed in the side portion to the upper portion of the dry-well volume and an annular clean water pool is closely disposed above the suppression pool via an insulating wall. Since the above-described two pools are connected to each other by a heat pipe, the heating value radiated into the clean water pool at the time of a loss of coolant accident can be transmitted to the clean water pool via the heat pipe and it is removed. However, since only the heat pipe is immersed in the upper portion of water in the suppression pool, the heat transferring effect by means of the heat pipe can be excessively deteriorated when water in the suppression pool is injected into the reactor pressure vessel at the time of the loss of coolant accident and level of the suppression pool is thereby lowered.